ADM-XRC SDK 2.4.0 User Guide (Linux)
© Copyright 2001-2004 Alpha Data


DMA transfers

The local bus bridge in an ADM-XRC series card contains one or more DMA engines. Software running on the host can use these DMA engines for the rapid transfer of data to and from the FPGA, using API functions such as ADMXRC2_DoDMA.

The local bus protocol of a DMA-initiated burst is the same as that of a direct slave burst. Assuming demand-mode DMA is not used, a DMA-initiated burst is indistinguishable from a direct slave burst:

This can be a useful property, as it often permits an FPGA design to be tested first using direct slave transfers (for convenience), and later on with DMA transfers (for throughput).

So far, this discussion has neglected demand-mode DMA. Although the basic burst protocol remains the same, the FPGA can distinguish between a direct slave burst and a demand-mode DMA burst because the sideband LDACK# signal is active in a demand-mode DMA burst. For a more complete discussion of demand-mode DMA, click on the following topic:

Demand-mode DMA

 


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